The invention relates to a method for locating a transmitter and receiver device, as used for example in automotive engineering for passive access control.
An operator for example carries a transmitter and receiver device, possibly in the form of an ID unit such as a key, a key tag, a smartcard, a chipcard, a timepiece, a remote control device or an implant, etc on or in proximity to their person.
This ID unit preferably causes specific actions, such as for example “open” or “lock the door locking system”, “release” or “lock antitheft device”, “start engine”, etc. to be executed without any further button operation but simply by proximity to a vehicle.
As the actions depend on and distinguish the degree of proximity, in particular “person inside vehicle” or “still outside vehicle within a certain range”, it is desirable to locate the position of the ID unit and therefore the person in relation to the vehicle. A transmitter and receiver device located inside the vehicle, in the form of a base station with a plurality of inductive antennas, is generally used for this, so that the position of the ID unit can be determined from the base station when received by a specific antenna (due to differing coverage).
The base station or control device sends out a number of successive requests via the different inductive antennas, which are generally integrated at different locations, and identifies the position of the ID unit, depending on the antenna by which the response signal of the ID unit was received.
The housing of a number of antennas at different positions in the vehicle, such as for example doors, rear windshield, vehicle roof lining, etc. is however disadvantageously complex and cost-intensive during vehicle manufacture and when fitted at a later date. Also transmitting at different powers is disadvantageously expensive with regard to the necessary hardware in the control device.